Longitudinal adaptations in neural and behavioral systems following hearing restoration using cochlear implants

Cochlear implants (CIs) restore hearing in people with severe-to-profound hearing loss, but how behavioral and neural adaptations unfold after implantation remains unclear, particularly during continuous speech processing. Most longitudinal studies of postimplant plasticity have used simple auditory stimuli, limiting insight into continuous-speech processing in complex environments. We followed 19 newly implanted adult CI users at activation and at 3, 6, and 12 mo after activation. At each session, participants completed speech recognition testing in quiet and noise, a spatial triple-digit test, hearing-related quality-of-life measures, and electroencephalography during an ecologically valid continuous-speech selective-attention task with competing distractors. Neural analyses focused on temporal response functions to task-relevant and task-irrelevant speech envelopes and changes in scalp field topography. Speech recognition improved over time, and spatial-separation benefits emerged by 6 mo. Neural tracking of task-relevant speech was stronger and emerged earlier than tracking of task-irrelevant speech, and scalp topographies changed significantly across sessions. Stronger task-relevant neural tracking was associated with better speech recognition, better spatial listening, and higher quality of life. The largest behavioral and neural gains occurred early after activation and plateaued by approximately 6 mo. These findings provide a functionally relevant account of postimplant adaptation and establish longitudinal continuous-speech neural tracking as a useful framework for studying rehabilitation after sensory restoration.